Creating A Plugin

Creating a Plugin

Overview

A Claude Code plugin packages reusable components (commands, agents, skills, hooks, MCP servers) for distribution. Create a plugin when you have components that work across multiple projects.

Don't create a plugin for:

• Project-specific configurations (use .claude/ in project root)
• One-off scripts or commands
• Experimental features still in development

Plugin storage locations:

• Development: Anywhere during development, installed via file:/// path
• User-level: ~/.claude/plugins/ (after installation)
• Project-level: .claude/plugins/ (project-specific installations)

Quick Start Checklist

Minimal viable plugin:

1. Create directory: my-plugin/
2. Create .claude-plugin/plugin.json with at minimum:

   {
     "name": "my-plugin"
   }
   

3. Add components (commands, agents, skills, hooks, or MCP servers)
4. Test locally: /plugin install file:///absolute/path/to/my-plugin
5. Reload: /plugin reload

Directory Structure

my-plugin/
 .claude-plugin/
    plugin.json              # Required: plugin manifest
 commands/                    # Optional: slash commands
    my-command.md
 agents/                      # Optional: specialized subagents
    my-agent.md
 skills/                      # Optional: reusable techniques
    my-skill/
        SKILL.md
 hooks/                       # Optional: event handlers
    hooks.json
 .mcp.json                    # Optional: MCP server configs
 README.md                    # Recommended: documentation

Critical: The .claude-plugin/ directory with plugin.json inside must exist at plugin root.

Component Reference

plugin.json Format

Minimal valid manifest:

{
  "name": "my-plugin"
}

Complete annotated manifest:

{
  "name": "my-plugin",                    // Required: kebab-case identifier
  "version": "1.0.0",                     // Recommended: semantic versioning
  "description": "What this plugin does", // Recommended: brief description

  "author": {                             // Optional but recommended
    "name": "Your Name",
    "email": "you@example.com",
    "url": "https://github.com/yourname"
  },

  "homepage": "https://github.com/yourname/my-plugin",
  "repository": "https://github.com/yourname/my-plugin",
  "license": "MIT",
  "keywords": ["productivity", "automation"],

  "commands": [                           // Optional: explicit command paths
    "./commands/cmd1.md",
    "./commands/cmd2.md"
  ],

  "agents": [                             // Optional: explicit agent paths
    "./agents/agent1.md"
  ],

  "hooks": [                              // Optional: inline hooks
    {
      "event": "PostToolUse",
      "matcher": "Edit|Write",
      "command": "npx prettier --write \"$CLAUDE_FILE_PATHS\""
    }
  ],

  "mcpServers": {                         // Optional: inline MCP configs
    "my-server": {
      "command": "${CLAUDE_PLUGIN_ROOT}/servers/my-server",
      "args": ["--port", "8080"],
      "env": {
        "API_KEY": "${API_KEY}"
      }
    }
  }
}

Key points:

• name is required, everything else is optional
• Use ${CLAUDE_PLUGIN_ROOT} to reference plugin directory
• Commands/agents auto-discovered from commands/ and agents/ directories if not listed explicitly
• Skills auto-discovered from skills/*/SKILL.md pattern

Creating Commands

File location: commands/my-command.md creates /my-command slash command

Nested commands: commands/feature/sub-command.md creates /plugin-name:feature:sub-command

Template:

---
description: Brief description of what this command does
allowed-tools: Read, Grep, Glob, Bash
model: sonnet
argument-hint: "[file-path]"
---

# Command Name

Your command prompt goes here.

You can use:
- $1, $2, etc. for positional arguments
- $ARGUMENTS for all arguments as single string
- @filename to include file contents
- !bash command to execute shell commands

Example implementation instructions...

Frontmatter fields:

• description - Brief description shown in /help
• allowed-tools - Comma-separated list: Read, Grep, Glob, Bash, Edit, Write, TodoWrite, Task
• model - Optional: haiku, sonnet, or opus (defaults to user's setting)
• argument-hint - Optional: shown in help text
• disable-model-invocation - Optional: true to prevent auto-run

Complete example (commands/review-pr.md):

---
description: Review pull request for security and best practices
allowed-tools: Read, Grep, Glob, Bash
model: opus
argument-hint: "[pr-number]"
---

# Pull Request Review

Review pull request #$1 for:

1. Security vulnerabilities
2. Performance issues
3. Best practices compliance
4. Error handling

Steps:
1. Use Bash to run: gh pr diff $1
2. Use Read to examine changed files
3. Use Grep to search for common anti-patterns
4. Provide structured feedback with file:line references

Focus on critical issues first.

Creating Agents

File location: agents/code-reviewer.md creates agent named "code-reviewer"

Template:

---
name: agent-name
description: When and why to use this agent (critical for auto-delegation)
tools: Read, Edit, Write, Grep, Glob, Bash
model: opus
---

# Agent Name

Detailed instructions and system prompt for this agent.

## Responsibilities
- Task 1
- Task 2

## Tools Available
- Read: File operations
- Grep: Code search
- Bash: Shell commands

## Workflow
1. Step 1
2. Step 2

Frontmatter fields:

• name - Required: kebab-case identifier
• description - Required: Max 1024 chars, used for auto-delegation
• tools - Comma-separated list of allowed tools
• model - Optional: haiku, sonnet, or opus

Complete example (agents/security-auditor.md):

---
name: security-auditor
description: Use when reviewing code for security vulnerabilities, analyzing authentication flows, or checking for common security anti-patterns like SQL injection, XSS, or insecure dependencies
tools: Read, Grep, Glob, Bash
model: opus
---

# Security Auditor Agent

You are a security expert specializing in web application security and secure coding practices.

## Your Responsibilities

1. Identify security vulnerabilities (SQL injection, XSS, CSRF, etc.)
2. Review authentication and authorization logic
3. Check for insecure dependencies
4. Verify input validation and sanitization
5. Review cryptographic implementations

## Workflow

1. **Scan for patterns:** Use Grep to find common vulnerability patterns
2. **Read suspicious code:** Use Read to examine flagged files
3. **Check dependencies:** Use Bash to run security audit tools
4. **Report findings:** Provide severity ratings and remediation steps

## Common Vulnerability Patterns

- SQL injection: String concatenation in queries
- XSS: Unescaped user input in templates
- CSRF: Missing CSRF tokens
- Auth bypass: Missing authorization checks
- Hardcoded secrets: API keys, passwords in code

## Reporting Format

For each finding:
- **Severity:** Critical/High/Medium/Low
- **Location:** `file:line`
- **Issue:** What's vulnerable
- **Impact:** What attacker could do
- **Fix:** How to remediate

Creating Skills

REQUIRED SUB-SKILL: Use writing-skills for complete guidance on skill structure, testing, and deployment.

Skills follow a specific structure.

File location: skills/my-skill/SKILL.md

Minimal template:

---
name: my-skill-name
description: Use when [specific triggers] - [what it does]
---

# Skill Name

## Overview
Core principle in 1-2 sentences.

## When to Use
- Symptom 1
- Symptom 2
- When NOT to use

## Quick Reference
[Table or bullets for common operations]

## Implementation
[Code examples, patterns]

## Common Mistakes
[What goes wrong + fixes]

Key principles:

• name uses only letters, numbers, hyphens (no special chars)
• description starts with "Use when..." in third person
• Keep token-efficient (<500 words if frequently loaded)
• One excellent example beats many mediocre ones
• Use writing-skills skill for complete guidance

Creating Hooks

File location: hooks/hooks.json or inline in plugin.json

Standalone hooks file:

{
  "hooks": [
    {
      "event": "PreToolUse",
      "matcher": "Bash",
      "command": "echo 'About to run: $CLAUDE_TOOL_NAME'"
    },
    {
      "event": "PostToolUse",
      "matcher": "Edit|Write",
      "command": "npx prettier --write \"$CLAUDE_FILE_PATHS\""
    },
    {
      "event": "SessionStart",
      "matcher": "*",
      "command": "${CLAUDE_PLUGIN_ROOT}/scripts/setup.sh"
    }
  ]
}

Hook events:

• PreToolUse - Before tool execution (can block)
• PostToolUse - After tool execution
• UserPromptSubmit - When user submits prompt
• Stop - When Claude finishes responding
• SessionStart - Session initialization
• SessionEnd - Session cleanup
• Notification - On Claude Code notifications
• SubagentStop - When subagent completes
• PreCompact - Before context compaction

Matcher patterns:

• Specific tool: "Bash"
• Multiple tools: "Edit|Write"
• All tools: "*"

Environment variables:

• $CLAUDE_EVENT_TYPE - Event type
• $CLAUDE_TOOL_NAME - Tool being used
• $CLAUDE_TOOL_INPUT - Tool input (JSON)
• $CLAUDE_FILE_PATHS - Space-separated file paths

Creating MCP Server Configs

File location: .mcp.json at plugin root or inline in plugin.json

Standalone .mcp.json:

{
  "mcpServers": {
    "database-tools": {
      "command": "${CLAUDE_PLUGIN_ROOT}/servers/db-server",
      "args": ["--config", "${CLAUDE_PLUGIN_ROOT}/config.json"],
      "env": {
        "DB_URL": "${DB_URL}",
        "API_KEY": "${API_KEY:-default-key}"
      }
    },
    "web-scraper": {
      "command": "npx",
      "args": ["web-mcp-server", "--port", "3000"]
    }
  }
}

Configuration fields:

• command - Executable path or command name
• args - Array of arguments
• env - Environment variables (supports ${VAR} or ${VAR:-default})

Special variable:

• ${CLAUDE_PLUGIN_ROOT} - Resolves to plugin root directory

Setting Up Dev Marketplace

For local development, create a marketplace to organize your plugins:

File: dev-marketplace/.claude-plugin/marketplace.json

{
  "$schema": "https://anthropic.com/claude-code/marketplace.schema.json",
  "name": "my-dev-marketplace",
  "version": "1.0.0",
  "owner": {
    "name": "Your Name",
    "email": "you@example.com"
  },
  "metadata": {
    "description": "Local development marketplace for my plugins",
    "pluginRoot": "./plugins"
  },
  "plugins": [
    {
      "name": "my-plugin-one",
      "version": "1.0.0",
      "description": "What this plugin does",
      "source": "./plugins/my-plugin-one",
      "category": "development",
      "author": {
        "name": "Your Name",
        "email": "you@example.com"
      }
    },
    {
      "name": "my-plugin-two",
      "version": "0.1.0",
      "description": "Experimental plugin",
      "source": "./plugins/my-plugin-two",
      "category": "productivity",
      "strict": false
    }
  ]
}

Directory structure:

dev-marketplace/
 .claude-plugin/
    marketplace.json
 plugins/
     my-plugin-one/
        .claude-plugin/
           plugin.json
        commands/
     my-plugin-two/
         .claude-plugin/
            plugin.json
         agents/

Install dev marketplace:

/plugin marketplace add file:///absolute/path/to/dev-marketplace
/plugin browse
/plugin install my-plugin-one@my-dev-marketplace

Plugin entry fields:

• name - Required: plugin identifier
• source - Required: relative path or git URL
• version - Recommended: semantic version
• description - Recommended: brief description
• category - Optional: development, productivity, security, etc.
• author - Optional: author details
• strict - Optional: default true (requires plugin.json), set false to use marketplace entry as manifest

Source formats:

// Local relative path
"source": "./plugins/my-plugin"

// GitHub repository
"source": {
  "source": "github",
  "repo": "owner/repo"
}

// Git URL
"source": {
  "source": "url",
  "url": "https://gitlab.com/team/plugin.git"
}

Naming Conventions

Use kebab-case everywhere:

• Plugin names: my-awesome-plugin
• Command names: review-code
• Agent names: security-auditor
• Skill names: test-driven-development

Filename mapping:

• commands/my-command.md � /my-command
• commands/project/build.md � /plugin-name:project:build
• agents/code-reviewer.md � agent name code-reviewer
• skills/my-skill/SKILL.md � skill name my-skill

Testing Locally

Development workflow:

1. Create plugin structure:

   mkdir -p my-plugin/.claude-plugin
   echo '{"name":"my-plugin"}' > my-plugin/.claude-plugin/plugin.json
   

2. Add components (commands, agents, skills)

3. Install locally:

   /plugin install file:///absolute/path/to/my-plugin
   

4. Test functionality:

   /my-command arg1 arg2
   # Use Task tool with your agent
   # Use Skill tool with your skill
   

5. Iterate:

   • Edit plugin files
   • Run /plugin reload
   • Test again

Using dev marketplace:

1. Create marketplace structure
2. Add marketplace:

   /plugin marketplace add file:///absolute/path/to/dev-marketplace
   

3. Browse and install:

   /plugin browse
   /plugin install my-plugin@my-dev-marketplace
   

Common Mistakes

Distribution

For production/team use:

1. Push plugin to Git repository (GitHub, GitLab, etc.)
2. Create or update team's marketplace repository
3. Add plugin entry to marketplace.json
4. Team members install:

   /plugin marketplace add user-or-org/marketplace-repo
   /plugin install plugin-name@marketplace-name
   

For public distribution:

Refer to official Claude Code documentation for publishing to public marketplaces.

Reference Links

• Official plugin docs: https://docs.claude.com/en/docs/claude-code/plugins
• Plugin reference: https://docs.claude.com/en/docs/claude-code/plugins-reference
• MCP servers: https://docs.claude.com/en/docs/claude-code/mcp-servers